Former cruiserweight champion Tony Bellew is no stranger to Oleksandr Usyk.

In 2018, Bellew challenged Usyk for the undisputed cruiserweight crown. The Ukrainian boxer brutally knocked Bellew out in the eight round. Bellew would retire in the aftermath.

Now at heavyweight, Usyk is one belt away from becoming the undisputed champion in a second weight class.

On Saturday night in Poland, Usyk will defend the WBO, IBF, IBO, WBA heavyweight belts against Dubois.

In his last fight, Dubois was dropped three times by Kevin Lerena. He was able to weather the storm to stop Lerena in the third round.

Based on his last performance against Lerena, and the 2020 knockout loss to Joe Joyce, Bellew believes a victory by Dubois would easily become one of the biggest upsets in boxing history.

“100 percent [Dubois winning would be one of the biggest upsets ever]. Without a shadow of a doubt. Going off the form of Daniel Dubois, he quit against Joe Joyce and he was on the brink of getting done by Lerena in the last fight he had and Lerena is not even in the same stratosphere as Oleksandr Usyk," Bellew told Talk Sport.

“So, he was made to quit by Joe Joyce and he’s very nearly came up short against Lerena, so to go from those kind of levels to Oleksandr Usyk, the former undisputed cruiserweight champion and current unified heavyweight champion, it would be monumental.”

In 1990, James ‘Buster’ Douglas pulled off what many observers view as the biggest upset in boxing history when he knocked out Mike Tyson in Japan.

Dubois defeating Usyk would be just as big, says Bellew.

“It would be along the same lines as Buster Douglas vs Mike Tyson in my opinion,” Bellew said. “He purely has one opportunity and one chance only and that’s a puncher’s chance, that is the only chance I’d give him to be totally honest.”